After his arrival at the University of Marburg, Papin exhibited to his colleagues in the faculty a modification of Huyghens's gunpowder-engine, in which he had endeavored to obtain a more perfect vacuum than had Huyghens in the first of these machines. Disappointed in this, he finally adopted the expedient of employing steam to displace the air, and to produce, by its condensation, the perfect vacuum which he sought; and he thus produced _the first steam-engine with a piston_, and the first piston steam-engine, in which condensation was produced to secure a vacuum. It was described in the "Acta" of Leipsic,[28] in June, 1690, under the title, "Nova Methodus ad vires motrices validissimas leri pretio comparandeo" ("A New Method of securing cheaply Motive Power of considerable Magnitude"). He describes first the gunpowder-engine, and continues by stating that, "until now, all experiments have been unsuccessful; and after the combustion of the exploded powder, there always remains in the cylinder about one-fifth its volume of air." He says that he has endeavored to arrive by another route at the same end; and "as, by a natural property of water, a small quantity of this liquid, vaporized by the action of heat, acquires an elasticity like that of the air, and returns to the liquid state again on cooling, without retaining the least trace of its elastic force," he thought that it would be easy to construct machines in which, "by means of a moderate heat, and without much expense," a more perfect vacuum could be produced than could be secured by the use of gunpowder. [28] "Acta Eruditorum," Leipsic, 1690. [Illustration: FIG. 17.--Papin's Engine.] The first machine of Papin (Fig. 17) was very similar to the gunpowder-engine already described as the invention of Huyghens. In place of gunpowder, a small quantity of water is placed at the bottom of the cylinder, _A_; a fire is built beneath it, "the bottom being made of very thin metal," and the steam formed soon raises the piston, _B_, to the top, where a latch, _E_, engaging a notch in the piston-rod, _H_, holds it up until it is desired that it shall drop. The fire being removed, the steam condenses, and a vacuum is formed below the piston, and the latch, _E_, being disengaged, the piston is driven down by the superincumbent atmosphere and raises the weight which has been, meantime, attached to a rope, _L_, passing from the piston-rod over pulleys, _T T_. The machine had a cylinder two and a half inches in diameter, and raised 60 pounds once a minute; and Papin calculated that a machine of a little more than two feet diameter of cylinder and of four feet stroke would raise 8,000 pounds four feet per minute--i. e., that it would yield about one horse-power.